The microstructure and oxidation behavior were investigated in Al and Cr co-deposited diffusion coatings prepared by the pack cementation process. The composition (in wt.%) of the packs was 3NH4Cl-xAl-(25-x)Cr-72Al2O3 with different Al levels (x = 0.5, 1.2, 4, and 10). After the heat-treatment process, the corresponding microstructure of the coatings was Cr + Cr2Ni3 + Al-rich phase, Cr + Cr2Ni3, Cr + NiAl + Ni3Al and NiAl + AlCr2, respectively. The isothermal oxidation tests were performed at 950 °C for up to 100 h in air, and the oxidation kinetic curves were obtained. It indicated that the coatings formed in the packs containing 1.2 wt.% Al had the lowest weight gain, while the weight gain of the coating formed in the packs having 4 wt.% Al was the largest. The presence of Cr in Al and Cr co-deposited coatings promotes Al2O3 generation. The formation mechanisms of Al + Cr co-deposited coatings and the effect of Cr in different types of coatings during the oxidation process were discussed.
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This is a manuscript of an article published as Lin, R. Q., C. Fu, M. Liu, H. Jiang, X. Li, Z. M. Ren, A. M. Russell, and G. H. Cao. "Microstructure and oxidation behavior of Al+ Cr co-deposited coatings on nickel-based superalloys." Surface and Coatings Technology 310 (2017): 273-277. DOI: 10.1016/j.surfcoat.2016.12.096. Posted with permission.